Ladder extension



FIG. 1 is a front elevational view of a ladder extension, the broken lines showing a ladder is for illustrative purposes only and forms not part of the claimed design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a right side view thereof;

FIG. 4 is a rear view thereof; and,

FIG. 5 is a front view thereof. 

The ornamental design for a ladder extension, as shown and described. 